Upload
others
View
4
Download
0
Embed Size (px)
Citation preview
Definitions
What is allergy?
Is allergy different to hypersensitivity?
Is there more than one kind of allergy?
Not every unexpected
reaction is Allergy
Hypersensitivity (abnormal response to a substance)
Allergic Non-allergic immune mediated not immune mediated
mechanisms understood mechanisms usually obscure
Role of IgE in Allergy (Allergy Antibodies)
Allergy (immunologic mechanism)
IgE-mediated Not IgE-mediated
Atopic Not atopic
e.g. drugs, insect stings
e.g. eczema, coeliac disease
Allergy versus intolerance
Food allergy: adverse reaction with
immune mechanism
Food intolerance: non immune-
mediated
Pre-formed chemicals:
histamine, tryptase, heparin
Newly generated:
leukotrienes,
prostaglandins
cytokines
Allergen-
specific IgE
IgE (allergy antibodies)
and Mast Cells
Histamine actions Allergy symptom
Irritation of nerve endings Itch
Leaky capillaries Urticaria / angioedema
Spasm of airways Asthma
Hypersecretion Runny Nose, eyes
Recruitment of immune cells Delayed recurrence
Sensitisation vs Allergy
• Allergy is a 2-step process:
1 Allergic sensitisation
(IgE produced to an allergen)
2 Allergic reaction / symptoms on exposure
Allergy testing
• Only to help confirm a plausible allergy
• Plausible: – Sneezing and itchy eyes in June
– Hives and wheeze 10 minutes after a bee sting
• Implausible: – Wakes with lip swelling day after eating nuts
– Sneezing from Lillies and other strong smells
– Fatigue after eating white bread
Ways of detecting
allergen-specific IgE
• Skin prick test
• Specific IgE in blood
– “RAST” test
• Challenge - the gold standard
• Quick, cheap, high patient impact
• Suitable for “unusual” allergens
• Good for excluding allergy
• Problems with eczema and dermographism
• False negatives in some circumstances
• Rare (<1:1000) systemic reactions
Skin Prick Testing
• Good for patients on anti-histamines and who have dermographism
• Reaction thresholds described for some food allergens
• Relatively expensive, delay in result
• False negatives in some circumstances
• Insignificant (weak) positive results
Specific IgE Blood Testing
Allergy tests cannot...
….be used for allergy screening
….predict likelihood or severity of reaction
….replace a careful clinical history
….identify causes or triggers for eczema
….be used to investigate medically unexplained
symptoms
Would you do an allergy test?
• Bloating and wind after eating white bread
• Wheezing and rash 5 mins after an insect sting
• Sneezing after eating mints
• Woke up with hives; ate strawberries previous
evening
• Severe diarrhoea after 3 days of amoxycillin
New Allergy – is it or isn’t it?
• 36 year-old woman with first episode urticaria
• Sudden onset at work
– 1 hour after lunch (prawn sandwich)
– Lip swelling
– Took colleague’s cetirizine, settled in ~2 hours
• Review 3 weeks later: 6 more episodes
– 1 on the day after ?prawns in curry
– 2 when colleagues eating nuts / prawns
– 1 ?new skin cream
Skin patch tests
• For diagnosis of contact eczema
• usually applied to back
• read at 48 hours
• nickel, lanolin, make-up, fragrances etc
You cannot diagnose Allergy by….
• Vega testing
• Hair analysis
• Blood specific IgG
• Kinesiology
• ALCAT testing
• Leucocytotoxicity
No such thing as an intolerance test
Allergy in West Midlands
• 5 centres with
Immunologist
• Comprehensive
allergy service
• Immunotherapy
• Network